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elm make hang then runaway memory usage from orphan process #2241

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javanwood opened this issue Jan 19, 2022 · 3 comments · Fixed by Zokka-Dev/zokka-compiler#20 · May be fixed by #2330
Open

elm make hang then runaway memory usage from orphan process #2241

javanwood opened this issue Jan 19, 2022 · 3 comments · Fixed by Zokka-Dev/zokka-compiler#20 · May be fixed by #2330

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@javanwood
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Quick Summary: Compilation hangs and an elm process remains active after <ctrl-c>. Memory usage of this process reaches >16GB (memory available to system) which bogged down my system.

SSCCE

module Main exposing (..)

foldMap : (a -> b) -> (a -> c) -> (b -> c -> c) -> a -> c
foldMap fab fac fbc a = fac a

break : Float -> (Float, Float)
break input = foldMap identity (\x -> (x, x)) (\( low, high ) x -> ( min low x, max high x )) input
  • Elm: Elm 0.19.1
  • Browser: NA
  • Operating System: macOS 11.4

Additional Details

elm make hangs after printing Compiling .... The orphan elm process only continues if waiting for longer than 5-6 seconds before using to cancel the elm make command.

When changing (\( low, high ) x -> to (\x ( low, high ) -> the snippet compiles as expected, and changing ( min low x, max high x ) to ( x, x ) results in the compiler error `foldMap` needs the 4th argument to be: ( ∞, ∞ ).

Came across this writing a foldMap to calculate the min and max of a List Float but have simplified to get a minimal reproduction.

Love your work!
@github-actions
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Thanks for reporting this! To set expectations:

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  • Ask questions in a community forum. You will get an answer quicker that way!
  • If you experience something similar, open a new issue. We like duplicates.

Finally, please be patient with the core team. They are trying their best with limited resources.

@maxime-didier
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Hello,

We encountered the same problem in our code after I mistakenly swapped the arguments of the set function in a lens. It looks to me that we encountered the same typechecker bug:

module Main exposing (..)

type alias Lens a b =
  { get : a -> b
  , set : b -> a -> a
  }

oopsLens : Lens { b | oops : a } b
oopsLens = Lens .oops (\x oops -> { x | oops = oops })

@lue-bird lue-bird mentioned this issue Aug 9, 2022
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@ccomb ccomb mentioned this issue Aug 14, 2022
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@pete-murphy
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pete-murphy commented Jan 9, 2024 •
edited
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Ran into a similar issue, though not from mistakenly swapping arguments, this was from a use of elm-form that I thought would actually compile. Boiled it down to

module Main exposing (..)


type X r
    = X


f : X r -> X { r | y : () }
f _ =
    X


x : X { z : () }
x =
    X


example : ()
example =
    x
        |> (if True then
                f

            else
                identity
           )
        |> always ()

That causes elm make to hang and balloon in memory usage (even after exiting with Ctrl+c).

@changlinli changlinli mentioned this issue Jul 16, 2024
Merged
changlinli added a commit to changlinli/elm-compiler that referenced this issue Jul 17, 2024
@changlinli
Minimal fix for issue elm#2241
248696f 
This fixes elm#2241

Preliminary testing seems to indicate this isn't as bad of a slowdown as
it may seem. For more details see Zokka-Dev/zokka-compiler#20

This is meant as a reference PR for other people working on the Elm
compiler.
@changlinli changlinli linked a pull request Jul 17, 2024 that will close this issue
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3 participants
@javanwood @pete-murphy @maxime-didier